This invention relates generally to a docking apparatus and method for spacecraft, and is particularly concerned with a docking apparatus and method enabling two spacecraft to be docked in a manner such that the first spacecraft is canted with respect to the second spacecraft so that mechanical interference between the two spacecraft is avoided.
Various types of apparatus have been proposed for accomplishing a temporary or permanent mechanical connection between two spacecraft. Such apparatus offer a practical means for assembly of a spacecraft, for the logistic support and transfer of crew members while maintaining a pressurized environment, and for the mutual support of two spacecraft by sharing their individual facilities and capabilities.
In its nominal configuration, a spacecraft typically has no means for docking with another spacecraft. For example, the Space Transportation System (also referred to as the Space Shuttle Orbiter) developed in the United States by the National Aeronautics and Space Administration (NASA) initially included plans for a docking adapter to be installed when needed in the payload bay of the Shuttle vehicle to provide a mechanical means for docking with another spacecraft and a pressurized passageway for crew transfer. The planned docking adapter was to include a pressure-tight port which would be attached to the exit port at the rear of the Shuttle vehicle cabin, and a further port to effect a structural and pressure-tight link with a similar mechanism on a second spacecraft. The docking adapter was to have a structural support of the same type as that used for payloads placed in the payload bay, as well as an additional exit port into the payload bay. Prior to docking, the docking adapter was to be telescoped vertically from its stowed position beneath the payload bay doors to a point beyond the top of the Shuttle vehicle cabin, in order to establish a clearance between the Shuttle vehicle and the docking spacecraft. At the end of the docking period, and after the spacecraft was released, the mechanism was to be retracted to its stowed position to allow the payload bay doors to be closed. However, the extension and retraction mechanism was seen as an objectionable liability in that it would be heavy and costly to develop; there was a risk in that a failure of the adapter to retract would preclude the closing of the payload bay doors and hence would imperil the Shuttle vehicle's return to earth. For various reasons, the plans for a retractable docking adapter were never realized by NASA.
Accordingly, a need has arisen for a safe and reliable docking apparatus to enable docking operations between two spacecraft. Such operations include the passage of crew members between the spacecraft for crew-tended operations and logistical support, the assembly or structural expansion of spacecraft, the addition or exchange of modules containing expendable supplies and equipment needed for space-borne experiments and manufacturing processes, and the on-orbit repair and maintenance of spacecraft. In the future, large free-flying spacecraft requiring assembly and resupply in orbit, such as the proposed NASA Space Station, will require all of the above operations to be provided by a space vehicle and crew on a frequent basis. As these operations are to be implemented by crew members moving between two spacecraft, they are best accomplished in what is known as a shirt-sleeve environment, that is, in a pressurized, earth-like environment that allows unrestricted passage of the crew between spacecraft without the need for pressure suits.
In order to be useful for the operations referred to above, the docking apparatus should preferably meet a number of objectives. One objective is that the docking apparatus be capable of attachment to the airlock compartment of a payload-carrying space vehicle, such as the NASA Space Shuttle, and that it allow unimpeded access to the vehicle's payload bay. Another objective is that the docking apparatus provide for the storage of equipment, supplies, and other items that are necessary to flight operations, and that the passageway within the docking apparatus enable the manual transport of such equipment and supplies by crew members passing through docking apparatus. A further objective is that the entire apparatus be capable of being carried in the payload bay and fully enclosed by the payload bay doors during launch and reentry; however, the apparatus must also provide a spacecraft docking interface that maintains a minimum clearance between the non-docking structures of the two spacecraft at their most proximate points. Another objective is that the docking apparatus must not endanger the closing of the payload bay doors, for such closing is essential to the return flight of the space vehicle. Retractable docking apparatus of the type proposed previously do not meet this objective, because a failure of the apparatus to retract would prevent the payload bay doors from closing and hence would make reentry impossible.
In addition to the objectives noted above, it is desirable that the docking apparatus comprise a load-bearing construction adapted for structural attachment to a payload retention apparatus of the space vehicle in which it is carried. This objective is three-fold. First, the docking apparatus is typically carried into orbit by the space vehicle and thus should be compatible with the existing vehicle payload retention apparatus. Second, the docking apparatus should, through its structure, restrain a docked spacecraft and transmit the inertial load of that spacecraft to the payload retention apparatus. Third, a major portion of the docking apparatus should be detachable from the space vehicle. This is important in cases where the docking apparatus must be disconnected from the space vehicle and remain on the docked spacecraft to reduce the weight burden on subsequent space vehicle flights, or to effect an emergency separation of the docking apparatus from the space vehicle. If these structural objectives are not met, the docking apparatus cannot be safely transported to and from orbit.
It is also desirable to provide a passageway to one or more attached payloads in the payload bay through a tunnel extending from the payload to the docking apparatus. An attached payload, such as the Spacelab payload developed jointly by NASA and the European Space Agency (ESA), can support shirt-sleeve conditions when linked to the cabin of the Shuttle vehicle by such a tunnel. Hence, the need exists for a docking apparatus which can be joined to such a tunnel in order to extend a pressurized passageway to the attached payload.